## Thursday, June 9, 2016

### The scientific mistake in The Matrix

Let's start with a summary of the plot of the famous science fiction movie The Matrix, directed in 1999 by the Wachowski brothers, the first of a trilogy:
During the twenty-first century, as a result of a total war between human beings and artificial intelligence machines, the humans are defeated. As a result of the war, the Earth is caught in a nuclear winter and sunlight cannot reach the surface. To find an alternative energy source, which they need to ensure their operation, the machines collect the human survivors and put them in a state of suspended animation to extract energy from their bodies, entertaining their minds with a virtual reality program (The Matrix) that makes them live in a world similar to that of 1999. Some of the humans escape that fate and carry out a guerrilla war against the machines, using the algorithms in The Matrix to obtain superpowers in the virtual reality world. One of the free humans (the main character, an exceptional hacker played by Keanu Reeves) manipulates The Matrix in such a way that, at the end of the film, he is hailed as the chosen one, who has been sent to save mankind from slavery.
During the last years when I taught, I used to pose my students the following problem:
What is the most important scientific mistake in The Matrix?

Not many managed to solve it. And yet, the error is obvious. At least, so it seems to me. Let us look at the solution:
·         The human body is not a source, but a sink of energy. To keep alive, we must be provided every day with a certain amount of energy (enough to maintain the basal metabolic rate), usually calculated, on average, as 2000 kilocalories per day. We get this energy from food.
·         To keep human beings alive, the machines would have to provide every day an amount of energy approximately equal to the product of the average basal metabolism by the number of human beings in a state of suspended animation. In other words, they would have to give them food. Humans would play the role of transducers, converting chemical energy (food) into heat, which in turn would be transformed into electrical energy. But we know that there are no perfect thermodynamic processes, so there is a waste of energy in each intermediate step in the transformation.
·         For the machines, it would be much more practical to dispense altogether with humans and transform directly the chemical energy of food into electrical energy. Thus two steps of energy conversion would be eliminated, greatly increasing the efficiency of the process.
·         If they did that, they would also gain additional benefits, as the ultimate elimination of the danger posed by those humans who, as the protagonist, escape control and become dangerous enemies. Nor would they need to maintain expensive devices to keep them in a state of suspended animation, or the computer support of the virtual reality system, which would also consume energy, further reducing the efficiency of the procedure, which would probably become ridiculous, if not negative.
·         Finally, nowhere in the film is said where the machines get enough food to keep their human slaves alive. In the absence of solar or other energy, it could not be cultivated.
In conclusion: the super-intelligent machines in The Matrix were not so smart. I can easily think of other energy sources they could have used more efficiently to ensure their survival, such as tidal or geothermal energy. According to the film, the crust of the Earth had been deeply excavated, probably almost to the level of the mantle, whose heat could be used as a virtually inexhaustible source of energy.

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Manuel Alfonseca